1. Field of the Invention
The present invention relates to an optical communications module used in a communications device that uses optical fiber. More particularly, the invention relates to a compact, highly-integrated optical transmission module utilizing wavelength-division multiplexing (WDM).
2. Description of the Related Art
Optical transmission systems using wavelength-division multiplexing (WDM) technology are being adopted as a method to economically transmit more information. Wavelength-division multiplexing systems simultaneously use a plurality of optical signals of different wavelengths to multiplex signals on a single optical fiber, thus making it possible to dramatically increase the quantity of information transmitted over optical fiber. These systems utilize the property that optical beams of differing wavelengths are mutually non-interfering. Consequently, it is important that the optical beams in a WDM optical communications module have fixed wavelengths.
However, the emission wavelengths of the electro-absorption (EA) modulator integrated laser diode (hereinafter abbreviated as LD) element used in wavelength-division multiplexing optical transmission modules exhibits a temperature dependency (approximately 0.1 nm/° C.). Consequently, an ATC (automatic temperature control) circuit is used, the ATC comprising temperature detection elements (i.e., a thermistor) and a cooling device using Peltier or similar elements or the like, housed in a metal case. The ATC is used to equalize the temperatures of the thermistor and the LD over a wide temperature range, and thus ensure that the optical beams maintain steady wavelengths.
In addition, other efforts are being made to equalize the temperatures of the thermistor and the LD over a wide temperature range and ensure that the optical beams maintain steady temperatures by using methods such as those of Patent Document 1.
Patent Document 1: JP-A-2001-244545